This invention relates to a water-cooled exhaust system for a watercraft and more particularly to an improved system of this type that will ensure adequate cooling and prevent against the likelihood of water entering the engine through its exhaust system.
As is well known, the treatment of the exhaust gases from the powering internal combustion engine of a watercraft present a number of problems. With many types of watercraft, such as small personal watercraft, the watercraft is very compact in nature and the length of the exhaust system may not be adequate to afford sufficient silencing of the exhaust gases. In addition, because the exhaust system passes in substantial part through the hull of the watercraft, it is also desirable to ensure that the exhaust system is adequately cooled. Frequently, flexible pipes are employed in the exhaust system for vibration absorption and to permit relative thermal expansion. These flexible pipes are not able to withstand the temperature of the exhaust gases as they exit the engine. Therefore, it is desirable to ensure-that the exhaust gases are adequately cooled. In addition to the cooling of the exhaust system, the cooling of the exhaust gases also adds to their silencing.
For these reasons, it has been the practice to provide a cooling jacket around a portion or portions of the exhaust system. This cooling jacket frequently receives coolant from the engine cooling jacket or from the body of water in which the watercraft is operating for its cooling purposes. Rather than circulating this cooling water through a heat exchanger, as is typical with land vehicles, the water is normally returned back to the body of water in which the watercraft is operated. Frequently, this is done by discharging the water from the cooling jackets into the exhaust conduit which is cooled so that it will pass to the atmosphere along with the exhaust gases.
Although this type of system has the advantages of simplicity and additional cooling of the exhaust gases, it raises a possibility that water may flow backwardly through the exhaust conduit to the engine through the exhaust ports. This is obviously not desirable.
It is, therefore, a principal object of this invention to provide an improved exhaust system for a watercraft.
It is a further object of this invention to provide an improved water-cooled exhaust system for a watercraft wherein at least a portion of the cooling water is discharged into the atmosphere with the exhaust gases flowing through the exhaust conduit.
It is a further object of this invention to provide an improved water-cooled exhaust system for a watercraft that will ensure that water cannot enter the engine through the exhaust system.
One way in which the exhaust system is cooled is to provide a cooling jacket around at least a portion of the exhaust conduit. Frequently, this cooling jacket is formed by using a double-wall pipe section with an inner member, an outer member spaced from the inner member and the space therebetween forms the cooling jacket. It has been the normal practice to terminate the length of the inner member short of the length of the outer member with this area where the lengths differ being the point where water is discharged from the cooling jacket into the exhaust conduit. However, this is a point where water could enter the engine through the exhaust system.
It is, therefore, a still further object of this invention to provide an exhaust system having a cooling jacket formed by a double wall pipe section and wherein the water from the double wall pipe section is introduced into the exhaust conduit but well downstream of the end of the inner member.